1. Field of the Invention
The invention relates to a heat dissipation device and a power module.
2. Description of the Related Art
A power module according to the related art will be described. A power module 500 shown in FIG. 6 includes a semiconductor element 12 joined to one face of an insulating substrate 14 and a heat dissipation device 116 joined to the other face side of the insulating substrate 14. A circuit is formed on one or both faces of the insulating substrate 14 according to a direct bonding aluminum (DBA) method, a direct bonding copper (DBC) method, or the like. The heat dissipation device 116 includes a radiator 120 and a heat dissipation plate 118. The heat dissipation plate 118 is provided if necessary. The heat dissipation device 116 radiates heat from the semiconductor element 12 that has been transferred via the insulating substrate 14, from the radiator 120. The radiator 120 includes a radiator fin 126.
In the described power module 500, a method of brazing the insulating substrate 14 and the heat dissipation device 116 (the heat dissipation plate 118), which generally differ in linear expansion coefficient, at high temperatures, such as about 600° C., and cooling them is applied in order to join these components to each other. In this case, the insulating substrate 14 and the heat dissipation device 116 contract in returning to a room temperature after having been brazed. The degree of contraction of the insulating substrate 14 and the heat dissipation device 116 differs depending on the difference in linear expansion coefficient the two components. That is, the heat dissipation device 116, which has a relatively large linear expansion coefficient (about 23×10−6/K in an example (aluminum) of a material with high thermal conductivity such as aluminum, aluminum alloy, copper, brass, or the like) contracts more than the insulating substrate 14, which has a relatively small linear expansion coefficient (about 4.5×10−6/K in an example (aluminum nitride) of a ceramic insulating material). Therefore, when the insulating substrate 14 and the heat dissipation device 116 are cooled to room temperature (e.g., 25° C.) according to a known cooling method such as cooling ice melting or the like, the radiator 120, which includes planar members 122 and 124, and the heat dissipation device 116 may become deformed, as shown in FIG. 7. When the radiator 120 and the heat dissipation device 116 are further deformed, a decline in the joint strength between the insulating substrate 14 and the heat dissipation device 116 and deterioration in the durability of the power module may result.
For example, as described in Japanese Patent Application Publication No. 2008-124187 (JP-A-2008-124187), Japanese Patent Application Publication No. 2006-294699 (JP-A-2006-294699), Japanese Patent Application Publication No. 2006-202884 (JP-A-2006-202884), and Japanese Patent Application Publication No. 2006-310486 (JP-A-2006-310486), there are various methods for preventing or reducing the extent of warping between an insulating substrate and a heat dissipation device and/or a heat dissipation plate.
JP-A-2008-124187 and JP-A-2006-294699 describe a plate material, in which a through-hole is formed, sandwiched between and joined to an insulating substrate and a radiator fin to relieve stress.
JP-A-2006-202884 describes that a heat dissipating plate is concavely warped beforehand toward an insulating substrate side to be restrained from being warped after being joined to the insulating substrate.
JP-A-2006-310486 describes a power module that includes a corrugated fin that is joined on only an insulating substrate side and is not joined on the opposite side of the insulating substrate.